This invention relates to a process for the removal of undesirable gaseous components from a hot waste gas, e.g., from a combustion process, containing sulfur dioxide and other contaminants, wherein the waste gas is cooled and scrubbed with a scrubbing agent selective for sulfur dioxide, as well as to an apparatus for conducting the process.
Hot waste gases are formed in the combustion of carbon-containing fuels; these waste gases contain gaseous components which, for reasons of environmental protection, must not be emitted to the environment in a concentration above legal limits. Sulfur compounds, in particular, such as sulfur dioxide, produced in the combustion of fossil fuels, must be substantially completely removed from the waste gas. A process has been proposed in DOS No. 2,848,721 for the removal of such compounds wherein hot waste gas is cooled and then scrubbed with a so-called physical absorbent, i.e., no chemical reaction occurring. In this method, almost the entire sulfur dioxide contained originally in the waste gas is scrubbed out. The waste gas, freed of sulfur dioxide, is then exhausted into the atmosphere.
Whereas the aforesaid prior-art process serves merely for the removal of sulfur dioxide, in many cases the waste gas contains, besides sulfur dioxide, additional components, especially nitrogen oxides, which also must not be exhausted into the atmosphere. To solve the problem of nitrogen oxide pollution, many proposals have been made, e.g., U.S. Pat. No. 4,164,546, Welty, "Method of Removing Nitrogen Oxides from Gaseous Mixtures" and references cited therein. Specifically, there are several processes based on the catalytic reaction of nitrogen oxides with ammonia to produce nitrogen. The Welty U.S. patent also suggests processes involving the removal of both nitrogen oxides and sulfur dioxide; however the emphasis in this patent is on the simultaneous removal of nitrogen oxides and sulfur dioxide, and also on non-noble metal oxides, e.g., copper oxide and vanadium pentoxide as catalysts, with little or no emphasis on heat exchange efficiencies.